RF Tags can be used in a multiplicity of ways for locating and identifying accompanying objects, items, animals, and people, whether these objects, items, animals, and people are stationary or mobile, and transmitting information about the state of the of the objects, items, animals, and people. It has been known since the early 60's in U.S. Pat. No. 3,098,971 by R. M. Richardson, that electronic components on a transponder could be powered by radio frequency (RF) power sent by a "base station" at a carrier frequency and received by an antenna on the tag. The signal picked up by the tag antenna induces an alternating current in the antenna which can be rectified by an RF diode and the rectified current can be used for a power supply for the electronic components. The tag antenna loading is changed by something that was to be measured, for example a microphone resistance in the cited patent. The oscillating current induced in the tag antenna from the incoming RF energy would thus be changed, and the change in the oscillating current led to a change in the RF power radiated from the tag antenna. This change in the radiated power from the tag antenna could be picked up by the base station antenna and thus the microphone would in effect broadcast power without itself having a self contained power supply. In the cited patent, the antenna current also oscillates at a harmonic of the carrier frequency because the diode current contains a doubled frequency component, and this frequency can be picked up and sorted out from the carrier frequency much more easily than if it were merely reflected. Since this type of tag carries no power supply of its own, it is called a "passive" tag to distinguish it from an active tag containing a battery. The battery supplies energy to run the active tag electronics, but not to broadcast the information from the tag antenna. An active tag also changes the loading on the tag antenna for the purpose of transmitting information to the base station.
The "rebroadcast" or "reflection" of the incoming RF energy at the carrier frequency is conventionally called "back scattering", even though the tag broadcasts the energy in a pattern determined solely by the tag antenna and most of the energy may not be directed "back" to the transmitting antenna.
Prior art tags have used electronic logic and memory circuits and receiver circuits and modulator circuits for receiving information from the base station and for sending information from the tag to the base station.
The continuing march of semiconductor technology to smaller, faster, and less power hungry has allowed enormous increases of function and enormous drop of cost of such tags. Presently available research and development technology will also allow new function and different products in communications technology.
One fundamental problem with passive tags is that the range is limited by the voltage picked up by the tag antenna and rectified by the tag power conditioning circuits. The voltage must be high enough to run the tag electronics, and the voltage is generally the limiting factor in determining the distance from the base station antenna at which the tags may be used. Even active tags having a battery to run the tag electronics are limited in the voltage picked up by the tag antenna. The antenna design, and the connection of the antenna to the RFID front end electronics, is critical in producing the voltage and the power needed to run the tag electronics. The pads on the semiconductor chip needed to connect the semiconductor chip or chips to the antenna wires have heretofore had dimensions necessary to mechanically support the bonded wires or the "bumps" on the chip to which the antenna wires were bonded. Large pads lead to high input capacitance. When the pad sizes were reduced to reduce the capacitance, it was found that the passivation material over the edges of the pad cracked when the pad was bonded to wires by well known thermal compression bonding, ultrasonic bonding, or laser bonding. It is probable that the passivation material would also crack under solder reflow, such as is used in "flip chip" bonding, and that the method of the invention would also be of value in soldering to the pad. The following application teaches a method and an apparatus to solve the cracking problem and reduce the input capacitance for RF signals. This is particularly valuable when the input is brought in from an RF antenna, since it is easier to tune the antenna for the lower capacitance.
The statement headed "The Problem" at the first page and the first two paragraphs on the second page of incorporated application Ser. No. 60/070,336 are referenced for a background explanation.